1. Field of the Invention
This invention relates to an LED (light-emitting diode) package structure, more particularly to a LED package structure with a thin design.
2. Description of the Related Art
Referring to FIG. 1, a conventional SMD (surface-mount device) LED package structure 9 generally places an LED chip 91 on a surface of a printed circuit board (PCB) 92, after which a transparent encapsulant 93 covers the LED chip 91 and is cured by a molding process, thereby sealing the LED chip 91.
The conventional LED package structure 9 has the following drawbacks:
1. When the transparent encapsulant 93 includes a phosphor material or is a colored encapsulant, a polarity of the package structure 9 cannot be directly distinguished, thereby causing difficulties in the assembly of the package structure 9 with a sired electronic device.
2. Since the LED chip 91 is placed on the surface of the printed circuit board 92, the thickness the transparent encapsulant 93 must be larger than that of the LED chip 91 so as to cover the same. As a result, the thickness of the whole package structure 9 is determined by the thicknesses of the printed circuit board 92 and the transparent encapsulant 93, making it very difficult to minimize thickness.
3. The printed circuit board 92 usually has an insulating layer 921 at a middle portion thereof, so that it has a poor heat-conductive effect. Thus, heat emitted by the LED chip 91 is transmitted through a metal layer 922 on the surface of the printed circuit board 92. As shown by the arrows in FIG. 1, heat is transmitted from a top surface of the printed circuit board 92 down to the sides, and from the sides to a lower surface of the printed circuit board 92, so that heat is transmitted along a long path and cannot be quickly dissipated. Accumulation of heat will adversely affect an illuminating efficiency and the lifetime of the LED chip 91.
Further, the currently available LED package structure 9 is mostly suitable for packaging only one LED chip 91, so that the range of application of the same is limited.
From the aforesaid description, it is apparent that the LED package structure 9 still has room for improvement.